Inner histone oligomeric associations and conformations have been examined as a function of solvent ionic strength and pH. These studies have shown that octamer dissociation can occur with minimal alteration of histone 2 and 3 structure. Chicken erythrocyte mononucleosomes (nu1) have also been examined as a function of solvent ionic strength and pH. These studies have indicated that many of the conformational transitions of isolated inner histones are analogous to transitions of nu1; i.e., the structural properties of the histones can be seen in the chromatin subunit. Crystals of nu1 have been examined by x-ray diffraction and parameters of the unit cell are being measured. Synthetic nu1 have been constructed from inner histone complexes with poly(dA-dT) poly(dA-dT). These particles are extremely homogeneous, and have permitted a subtle probing of the DNA conformation and stability by circular dichroism, thermal denaturation and enzymatic digestion. Electron microscope studies have been directed towards the localization of specific nuclear macromolecules in the three-dimensional space of nuclei and chromosomes, employing stereo-electron microscopy and immunoferritin labelling. Stereo-EM studies have been completed upon isolated chicken erythrocyte nuclei, and on whole chicken reticulocytes, employing various staining techniques.